An integrated circuit (‘IC’) device comprises a semiconductor die containing many IC components such as registers and functional blocks, interconnecting logic gates such as AND, OR gates and memory components such as flip-flops. Electrical conductor nets on the die connect the IC components together and to contact pads at the surface of the die. The IC device may have more than one power domain, each having its own power supply.
The IC die is housed in a package which supports and protects the IC die and provides external electrical terminals. The IC device is assembled on a support in a product using the package terminals to make electrical connections for logic signals and power supply between the contact pads of the IC and external circuits. The power supply connections of each power domain may have one or more corresponding package terminals.
Often, the IC package is of surface mount technology, which facilitates mounting the package directly on a support such as a printed circuit board (‘PCB’), for example. There are several types of surface mount package, including packages having electrical terminals which are short pins or leads of various styles, flat contacts or an array of solder balls (‘BGA’s), for example. Typically, the device is placed on a PCB that carries conductive pads in a pattern that matches the package terminals, and the assembly is then heated, either in a reflow oven or by an infrared heater, causing solder to melt, making the electrical connections between the package terminals and the PCB and securing the package mechanically to the PCB.
Whatever the type of package, the complexity of the IC necessitates extensive testing of the functioning of the IC by the IC manufacturer before it is delivered commercially for assembly, which may be performed by a customer, for example. Typically, this testing is performed by automatic test equipment (‘ATE’) having a high degree of automation and the IC device itself is designed to facilitate the operation of such ATE by techniques globally referred to as design-for-test. In addition, the customer usually tests the assembled product comprising a PCB, for example, with the IC mounted on it, if only to check the quality of the logic signal connections.
The tests are intended to eliminate as many defective devices and products as possible. However, they are also intended to avoid eliminating devices and products which would in fact function correctly or to identify products that could be reworked to function correctly.
A known test procedure includes the open-short test algorithm, which is implemented in many test equipments to detect logic signal connection failures. Another known test procedure is described in US patent specification U.S. Pat. No. 7,042,237 which detects incorrect logic signal connections of the device under test and also signals incorrect positioning of the device in the test interface, avoiding unjustified rejection of the device when an apparent device fault is in fact due to human error.